In heart failure, the heart does not pump blood as well as it should and fluid builds up in the lungs. The symptoms of heart failure include difficulty breathing, decreased ability to exercise, and leg swelling. Although many drugs help patients with heart failure, there is no cure. The condition is disabling and even fatal for many patients.
In patients with heart failure, conduction of electrical impulses through the heart is often abnormal. This abnormal conduction, in turn, can lead to uncoordinated contraction of the ventricles, the large pumping chambers of the heart. Cardiac resynchronization, or atrial-synchronized biventricular pacing, has been shown to be an effective treatment for patients with moderate-to-severe heart failure.
Cardiac resynchronization is a heart failure treatment that uses a special type of pacemaker to synchronize the contraction of the ventricles. Results from resynchronization therapy studies on patients with New York Heart Association (NYHA) class III and IV heart failure have demonstrated significant improvement in the quality of life, functional status, and exercise capacity. In these patients, cardiac resynchronization has also been shown to improve cardiac structure and function while significantly reducing the risk of worsening heart failure.
Another serious cardiac condition is atrial fibrillation (AFIB). AFIB is a debilitating rapid and uncoordinated or chaotic depolarization of the atria, resulting in irregular contraction of the ventricles. In this condition, the atria are not capable of efficient ejection of blood into the ventricles during atrial systole, and blood tends to collect and stagnate in the atria. Patients with chronic AFIB are generally placed on life long systemic anticoagulation medication to prevent the formation of blood clots in the non-functional atria. AFIB is a common ailment among the aging population.
An even more serious cardiac condition is ventricular fibrillation (VFIB). VFIB is a rapid and uncoordinated or chaotic depolarization of the ventricles. In this condition, the ventricles are not capable of efficient ejection of blood, often resulting in sudden death of the subject. Patients at risk for VFIB often receive an implanted cardiac defibrillator.
Both AFIB and VFIB can be caused by an ectopic focal stimulation source arising from aberrant cells in the myocardium. For example, in the majority of AFIB, the abnormal cells giving rise to the condition are located in or around the openings of the pulmonary veins. Both AFIB and VFIB can manifest as racetrack patterns of depolarization in which depolarization traverses an irregular path through the tissues. In both conditions, depolarization is no longer controlled by the sinus node.